E-Mag and the GRT EIS 4000 tach issue

The GRT EIS manual 7.6.1 says ?A 27 ohm resistor must be connected between the instrument and Mag P-lead as shown in figure 7 to protect the mag from being turned off by a failure in the instrument?.
The E-Mag Air installation drawing shows the tach output as a dedicated line, not the P-Lead.
Do I need a 27 ohm resistor between the EIS and the P-Mag?

I would say no. They are trying to protect a regular mag's P lead from a failure in the system causing the regular mag to stop functioning. The P lead in an EMag does not provide a tack signal so would not get connected to any instrument other than an ignition switch. The tach output signal of the Emag could be shorted to ground with out causing the mag to stop function IN ALL LIKELIHOOD. You should ask them. I have it going into an EI tach without a resistor. On the other hand if you want to hook it up today and don't want to wait, adding the 27 ohm resistor will not hurt anything.
One other thing, the output of the emag may need to be buffered to be the right voltage for your GRT. I think from memory the output is a 5 volt pulse. If GRT needs a 12 volt pulse you mey need to add a transistor to increase the pulse voltage. I recall seeing this in pmags paper work.

I just looked at their web site and the new model 114 emag has an optional tach voltage pulse, it can be set up for 5 volts or 12 volt pulses. The 113 model has 5 volt pulses.

Actually the 113 model

with the later firmware can be set up to deliver 12V as well.

No resistor required as you say its just a tach signal wire, not the P lead itself.

Simply find out what voltage the 4000 needs and set your Pmag up to that.

Frank